This invention will be discussed in relation to improvements in strainers used with wire in an electric security fence. However, a skilled person will appreciate that the principles of the present invention can be applied to tensioning lengths of other materials in different situations and is not necessarily limited to electric fences and/or wire.
Strainers have been in use for numerous years to aid the tensioning of wire in fences, such as those used in the farming or security industries. The fences can be either conventional or electrified.
Most current fence strainers utilise a ratchet pivotally attached to a strainer. The ratchet typically has a set of teeth around the circumference of the ratchet that interacts with a locking mechanism such as a pawl which is also attached to the main body of the strainer. The interaction between the teeth and the pawl allows the ratchet to be turned in one direction when tightening the wire, but not in the other direction. The pawl is usually engaged with the teeth of the ratchet due to gravity (or a spring) and held in place by the tension of the fencing wire once strained up and under tension.
Most security fences rely on a system where multiple wires are tensioned in parallel using strainers currently available in the art. Typically, the electrical current is passed from one wire to another wire using two clamps or crimps and a wire link (herein termed a conductive link). The conductive link is usually positioned near to the ratchet along the length of the adjacent wires. This results in an electric current passing through the adjacent fence wires to discourage people/animals from contacting the fence in fear of being shocked or electrocuted. Also, if a wire is cut or shorted out to an adjacent wire then monitoring electronics circuits can send a signal to a control system or sound an alarm indicating a security breach. However, these systems above have a number of disadvantages as discussed below.
Installation of the conductive links and strainers requires considerable time, skill and effort to provide the desired outcome. This dramatically affects the overall cost (due to man hours) in fence preparation, maintenance and replacement.
Furthermore, as the conductive link and strainer are separate units, the system described above can be untidy and unappealing to the onlooker. This can be an issue for property holders that require security fences, yet want to maintain an aesthetic appearance to their fence and property.
Wires in fences are prone to loosening over time (due to stretching), and the strainers are often periodically used to re-tension the wires; usually rotation of the ratchet will achieve this result.
However, the conductive links located between the wires can become uneven due to wire adjustment which can add to the untidiness of the fence. Fixing this unappealing feature requires further time, and ultimately cost.
Furthermore, as the conductive links are typically inflexible, the conductive links only have a certain amount of movement which will ultimately hinder the amount of possible adjustment of the wires. Again, re-adjustment of the conductive links to address this problem can take further time and effort.
Currently available systems can also present a risk that a perpetrator can cut the security wire upstream of the conductive link's position to avoid triggering an alarm. All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.
Throughout this specification, the word “comprise”, or variations thereof such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.